FIGS. 1-5 show a previously known blind fastener generally indicated at 20, here used to fasten members 22, 24, and 26 together. Fastener 20 comprises a generally tubular outer member 28 and setting means 30. Outer member 28, which is identical to the outer members shown in the other figures and is numbered with the same reference characters, is disposed along an axis 32 and has a first head 34 at one end, a coaxial, generally conical, purposefully radially expandable portion 36 at the other end, and a tubular portion 38 between said ends. Portion 36 has an apex 40 disposed within tubular portion 38. Axial slits such as 42, 44, and 46 extend along tube 38 and portion 36, cutting the region of tube 38 adjacent portion 36 and dividing that region into plural legs. An interior wall 50 within outer member 28 defines an internal passage in tube 38 passing through head 34 and tube 38 for access to the interior side of apex 40.
In the known structure, setting means 30 is a solid cylindrical pin having an outer face 52 that protrudes from head 34 before the fastener is set and an inner face 54 butting against apex 40. Before the fastener is set, as illustrated in FIG. 4, outer wall 56 is cylindrical, permitting the fastener to be inserted in apertures 58, 60, and 62 of workpieces 22, 24, and 26 so that portion 36 protrudes beyond the other side of the last aperture (62). The fastener is then set by driving outer face 52 axially toward apex 40. The inward travel of setting means 30 thus flattens portion 36 axially, forcing legs such as 64, 66, and 68 of outer member 28 radially outward to form a second head 72 having a greater diameter than aperture 62, thereby securing the fastener in place and clamping parts 22,24 and 26 together. The dimensions of setting means 30 and interior wall 50 are such that the fastener should not fall apart, whether before or after setting.
One difficulty with this structure is that the prior art setting means 30 has a limited degree of resilience and thus is frequently subject to loosening, especially in joined structures subject to vibration. If setting means 30 loosens and falls out, the shear resistance of fastener 20 is materially reduced. Another difficulty is the relatively high weight of pin 30 in relation to its shear strength.
Fasteners of the general type described above are also illustrated by the following U.S. patents: 2,398,532, issued to Keehn on Apr. 16, 1946; and 2,948,937, issued to Rapata on Aug. 16, 1960. U.S. Pat. No. 2,562,721, issued to Jakosky on July 31, 1951, shows a fastener having a similar shell, but set by hydraulic pressure. Somewhat less pertinent are the devices shown in U.S. Pat. Nos. 3,350,976, issued to Topf on Nov. 7, 1967; and 3,481,242, issued to the same inventor on Dec. 2, 1969.
French Pat. No. 2,306,782, issued to Raychem Corporation, discloses a settable fastener having a outer tubular piece shown in its FIG. 1C and an inner tubular member shaped much like a spring pin. The inner element is made from an alloy which has a memory, allowing it to undergo a change in shape when the temperature of the assembly is changed. This change allows the inner element to expand, thereby deforming the outer element to form the second head of the fastener. This construction has the disadvantage of requiring the application of heat to the inner member to set the fastener. The fastener shown in that patent apparently cannot be set by driving the inner element into the assembly.
Spring pins per se are also known, but have not been used according to the present invention.